The present invention relates to an apparatus and method for forcing a member through a material, especially where such materials exist in conjunction with a load bearing strata, either naturally occurring or man-made, and which transmits the reactive forces developed during use of the invention to the load bearing strata. More particularly, the present invention relates to a method and apparatus for obtaining material samples, such as soil samples, from under a structure or concrete slab.
A common work activity of geotechnical scientists and engineers is the analysis and evaluation of earth materials. For example, when a building structure has experienced distress to its foundation or to other elements of construction, information concerning the soils and other materials underlying the structure, as well as physical samples of those materials, is required for the analysis and evaluation of the distress.
It is well known in the geotechnical field that such samples should be "undisturbed" because sample disturbance increases the likelihood and degree of error in the assessment of in situ physical properties and characteristics of the material sampled. "Undisturbed" samples are commonly obtained by advancing a thin-walled tube, ranging in length from several inches to several feet and commonly called a "Chicago Tube" or a "Shelby Tube", into the soil or other material to be sampled. Once the tube is sufficiently advanced to contain a "plug" of the material to be sampled, it is withdrawn. That operation is repeated a sufficient number of times, using a number of such tubes, to create a continuous series of sample "plugs" which comprise the physical "undisturbed" samples of the materials through which the sample tube is forced. Upon completion of the sampling and retrieval operations, the plugs of soil are removed from the tubes and various tests performed to assess the properties of the material samples.
Although it is sometimes fairly easy to obtain such samples with truck-mounted, conventional drilling and sampling equipment, such equipment is relatively expensive to purchase and operate, and in many cases, space and other limitations, such as the need for venting the exhaust fumes of an internal combustion engine, prevent the entry of a relatively large, truck-mounted drilling rig into the location at which sampling must be conducted. Limitations of that nature are particularly acute when the sampling site happens to be within a building or other structure, for instance, when information might be required about the materials under a foundation slab after the slab has shifted or cracked. In such cases, the size of the truck-mounted drilling rig and the fumes produced by the truck's motor obviate its use and require the use of cumbersome hand-sampling methods.
Presently-utilized hand-sampling methods generally involve manually impact-driving the sample tubes into the sub-foundation materials with sledgehammers or dropweights. The sample tubes are generally attached to the end of a piece of pipe or other suitable rod for driving and, after being so driven, are extracted by manually impacting them out of the "hole" or, in some cases, using automobile jacks to jack against chains which are wrapped around the sample tube drive rod. After the samples are retrieved, they are extruded from the sample tube at a standby drill rig having extrusion capability or they are taken back to a laboratory for extrusion.
As is well known to those skilled in the art, the disadvantages of such hand-sampling techniques and equipment are many. They include, for instance, the extremely labor and equipment intensive nature of the techniques and difficulty, or even impossibility, of obtaining samples as the hardness of the sub-foundation materials increases. From an economic standpoint, only shallow samples can be obtained, and the tendency of the axis of advancement (or retraction) to wander (especially in harder materials) introduces additional variables into assessment of the samples and increases the amount of effort required. Further, even though the samples are supposed to be "undisturbed" samples, they are often severely disturbed due to the impacts required to advance and retract the sample tube. Sample quality is, therefore, unpredictable and erratic, worker fatigue is common and can be extreme, and injuries to the fingers and hands of the workers are commonplace. An additional limitation of such techniques is that they cannot be used to place various members or devices, such as penetrometers, stepped blade soil pressure transducers, piezometer tubes, and soil gas samplers for example, into the material for in situ assessment of the properties of the material because of the cumbersome nature of such techniques and the sensitivity of such members or devices to the impacts needed to advance them into the materials.
Although the above discussion refers in large part to methods for obtaining samples from beneath structures, the problems and limitations discussed are generally similar to those encountered whenever it is desired to advance or retract a device or member through a mass of material. Such operations are common in the geophysical, geological, and construction arts and include, but are not limited to, driving and the placement of members such as benchmarks, geophysical logging equipment, well points, well casings, and soil anchors for guy wires and retaining walls, as well as the penetrometers, pressure transducers, piezometer tubes, and soil gas samplers discussed above. It is, therefore, an object of the present invention to provide an apparatus which is adaptable for a number of purposes relating to advancing and retracting such a member or device(s) within a mass of material such as soil.
Further, although the above discussion refers primarily to performing an operation such as obtaining a soil sample from beneath a building foundation, it will be understood that the structure need not be a building foundation. Indeed, it is another object of the present invention to provide a small, portable device for forcing a member or device through a mass of material and which transmits the reactive forces resulting from the resistance of the material to the forcing of the member therethrough to the material or to a load bearing strata such as a concrete drain culvert, retaining wall, a naturally occurring rock foundation or other strata, or the strata found in and around the material through which the member is to be forced, as well as a floor, slab, foundation, or other elements of a building.
Further, so far as is known, no practical device or method is available for performing such operations on steeply sloped or overhead surfaces, or in enclosed or confined spaces. It is another object of the present invention to provide such an apparatus.
A further object of the present invention is to provide an apparatus which can be used to obtain tube-type soil or materials samples and to extrude those samples from the sample tube on-site, thus obviating the need for extrusion of the sample from the sample tube with a standby drill rig or at the lab, thereby enhancing the scientist's ability to direct an effective sampling program in the field.
It is another object of the present invention to provide an apparatus which can penetrate hard formations that hand-sampling methods cannot breach, can be adapted for setting benchmarks and their casings without the requirement of first drilling a pilot shaft, and can be utilized to place various devices and instruments, including, but not limited to, piezometer tubes, dutch cone penetrometers, other types of probes or bits, soil anchors, and soil pressure meters in the soil, as well as soil or other material sampling.
The advantages of such a device will be apparent to those skilled in the art from even the above-summarized brief description of the various uses and capabilities of the present invention. In short, the apparatus and method of the present invention saves time and money, eliminates manual hammer and drop weight methods, allows work in confined locations or locations that are otherwise inaccessible to conventional power equipment, and reduces the size of the crew required for performing the on-site operations necessary for the scientist or engineer to attain his or her objectives. The member can also be advanced further into the mass of materials than is currently possible with hand methods. Because the member, notably a sample tube, is smoothly forced straight into the materials worked upon, the undesirable effects of impacting, sample disturbance, and wandering of the axis of advancement are reduced. Operator fatigue is reduced and sample extrusion can be handled on-site.